1. Field of the Invention
The invention relates to a method for calculating a μ-slippage curve of a tire.
2. Description of the Related Art
The degree of safety is one of the most important features for the development of a tire and consequently for a vehicle using this tire.
One of the most important characteristics for the safety of a tire is the friction coefficient. The friction coefficient is a characteristic value of a tire describing the capacity of the tire to disperse energy during driving maneuvers in order to maintain the control of the vehicle during curve, braking or acceleration. Often this characteristic is called “grip” of the tire.
Normally car manufactures ask tire manufacturer to qualify a tire by using a braking test. By implementation of electronic control systems, the behavior of the friction coefficient in dependence on the relative sliding velocity of tire and road is a very important parameter to optimize braking distances and driving behavior of a car. For evaluating this dependence, the so called μ-slippage curve is used. The μ-slippage curve illustrates the relation between tire load and braking force in dependence on the relative velocity between tire and road. During the braking test the difference between velocity of the car and tire velocity is measured (slipping velocity) on a special trailer and the force induced on the tire axle in driving direction and vertical direction is measured and expressed as friction coefficient of the tire.
The μ-slippage curve is used for forecasting the braking behavior of a car. Moreover it is really important for adopting and designing the under- and oversteering behavior of a car during steering.
To make the conventional braking test it is required to produce a tire and to test the tire. The production of a tire is very expensive and time consuming. During the development of new compounds for tires, it is not possible to run the braking test for all possible variations of a new compound. However a selection of features of the used compound must be made based on laboratory tests. Normally the laboratory tests are basic tests executed on laboratory samples and do not describe directly the tire behavior. The selection of the used compound is made substantially based on the experience of the compound developing engineers.
Former methods for estimating a μ-slippage curve of a tire are based on calculations used constant values for the friction coefficient. However the comparison of the estimated μ-slippage curves based on constant values for the friction coefficient with real measurements on a tire shows the uselessness of such estimation methods.